1. Field of the Invention
The present invention generally relates to a disk drive, and more particularly, to a servo write technique that improves in head positioning accuracy.
2. Description of the Related Art
In the field of a disk drive that-is typified by a hard disk drive, recently, the disk drive has dramatically increased in recording density in order to meet a demand for its large capacity and downsizing.
In a disk drive, generally, the recording density (TPI: track per inch) of data tracks formed on a disk medium is heightened to improve the recording density of the disk medium. This is achieved by improving head positioning accuracy.
The head positioning accuracy necessitates improving both a servo control system for head positioning control and a servo track write technique for recording servo data for the head positioning control.
In the servo control system, a head is positioned in a target point on the disk medium in accordance with servo data read out of the disk medium by the head.
The servo track write technique is one for accurately writing servo data in specified areas (servo areas) on the disk medium usually using a servo track writer (STW) that is exclusively used for the technique.
The STW has a problem that the skew angle of the head erases servo data of adjacent tracks to cause an erase area. In the STW and disk drive, generally, the head is loaded onto a rotary actuator and configured to seek in the radial direction of the disk medium.
The skew angle is the absolute value of the inclination of the head with regard to the data tracks on the disk medium. The erase area occurs because one end of a magnetic gap of a write head protrudes toward an adjacent track.
The STW usually writes servo data while moving a servo head at ½ or ⅓ track intervals on the disk medium. Thus, the erase area becomes much easier to occur and results degrading the signal quality of servo data recorded on the disk medium. If, moreover, the TPI of the disk medium increases, the proportion of erase areas to data tracks also increases, with the result that the adverse affect of the erase areas becomes large.
In the field of a disk drive, a drive using a perpendicular magnetic recording method has recently been developed as a technique of increasing the recording density further. A disk drive of a perpendicular magnetic recording type employs a single pole type head as a write head. Even using such a single pole type head, an erase area is generated by the skew angle as described above.
A method of reducing the above erase area due to the skew angle of a head is proposed (see, for example, Jpn. Pat. Appln. KOKAI Publications Nos. 2000-268516 and 2001-189062).
According-to the method in the above Publications, servo data is written by seeking a head from the outermost radius of a disk medium to a position in the radial direction of the medium in which the skew angle is 0°. In other words, the respective operations are performed separately and selectively.
In the method in the above Publications, since all erase areas generated on the disk medium are overwritten, they can be deleted. However, no servo data can be recorded on an area close to the position in which the skew angle is 0°, thereby generating an area that cannot be used as a data track.
In the perpendicular magnetic recording method, it has been confirmed that an erase area can be reduced by devising a method of designing the pole of a single pole type head. In other words, since the width of the erase area is proportionate to the thickness of the pole, the erase area can be reduced by thinning the pole. If, however, the pole is thinned, the area of the pole decreases to lower the capability of recording of a write head.
There is another method of reducing an erase area by tapering a head into a trapezoid. In this method, too, however, a greatly tapered head reduces the area of the pole and thus lowers the recording capability of a write head. It is not easy to manufacture a greatly tapered trapezoidal head from its practical aspects.